Seismic data, such as pressure (P) wave and shear (S) wave data, is often used to model geological formations lying beneath the seafloor. Seismic data is particularly useful in the offshore energy industry to gain a better understanding of potential drill sites. For example, seismic data can be used to determine the existence of a fossil fuel reservoir, and whether such reservoir is capable of trapping such fuels by the existence of stratigraphic “traps” which prevent upward loss of the fluids.
Various techniques and associated instrumentation have been developed to acquire, or record, seismic data. One such marine technique comprises the use of streamers, which are recording devices that are towed behind a sea vessel. In practice, a source-firing event is used to create P-waves, which reflect off the geologic formations beneath the seafloor and back to the towed streamers. However, towed streamers are generally submerged a short distance from the sea surface, and therefore, are unable to record S-waves, which are unable to travel through seawater. Also, towed streamers are very vulnerable to damage, expensive and have numerous quality issues, such as induced noise from towing, and data degradation caused by mobile receiver points. Still further, towed streamers are linear in arrangement and, therefore, fail to provide sufficient samplings for gaining a true three-dimensional (3D) image of the targeted geologic formation.
Seafloor recording systems have been developed to overcome some of the problems associated with towed streamers. For example, ocean bottom cable, or OBC, systems have been used to gather seismic data. These systems generally utilize a cabled connection between seafloor recorders and a static control vessel on the sea surface. OBC systems improved the acquisition of seismic data by enabling the recording of S-wave data. However, such systems have been found to be unreliable because of the need to deploy and recover the cables on a daily basis, thereby increasing the likelihood of seawater ingress. Also, OBC systems, as with the towed streamers, are linear in arrangement and, therefore, fail to provide sufficient samplings for gaining a true 3-D image of the targeted geologic formation.
The inadequacies associated with towed streamers and OBC systems have lead to the development of ocean bottom seismic, or OBS, systems. OBS systems utilize seafloor recorders, which, unlike OBC recorders, are not cabled to the control vessel when deployed. Current OBS systems are excessively expensive and inefficient, which calls the commercial viability of such systems into question. For example, current OBS systems are unable to determine the heading (orientation) of the seafloor recorders without the use of a remote operated vehicle (ROV). Indeed, an ROV must be deployed for each seafloor recorder to determine the orientation of each seafloor recorder. As can be appreciated, the deployment and operation of an ROV for each seafloor recorder greatly increases the costs and time associated with gathering seismic data. In turn, the inefficiencies surrounding the use of ROVs prohibit the deployment of a sizable number of seafloor recorders. Consequently, current OBS systems do not provide sufficient data samplings for gaining a true 3-D image of the targeted geologic formation.